The present invention relates to a micro linear positioner, particularly developed for optical switches, and a manufacturing method for such micro linear positioners and/or optical switches. An electromagnetic coil moving a magnet between two latched positions in the device controls the switch-path of the positioner.
Many modern optical systems use light beams, usually laser-generated, to carry various types of information. Within the optical system, a light beam may alternate between travelling in free space and/or travelling in a fibre or another optical conductor. Amongst many other applications, the technology can be used for example to combine computers with mechanical devices such as sensors, valves, gears, mirrors, and actuators, etc. Many optical systems, such as fibre-optic micromechanical devices, e.g. in telecommunication systems etc. utilizing optical fibres, require the use of optical switches for selectively coupling signal sources to one or more destinations. In the field of micro-technology, micro-electromechanical systems (MEMS) switches formed on single-crystal silicon wafer substrata are used for the coupling of the signals. These optical switches are normally actuated by thermal, piezoelectric, or electrostatic means embedded in the silicon wafer substrate. However, many fibre-optic micromechanical devices do not fit that small order of magnitude, and micromechanical optical switches of larger dimensions are needed where thermal or piezoelectric actuators no longer can be used. Therefore in the field of fibre-optic communications, there is a need for electromechanical micro-actuated optical switches. The function of the switch is to direct/redirect laser beams from one channel to another within a maximum time of 10 ms. These switches are typically electromechanical and operate by moving a mirror or filter to either permit or deviate passage of a laser beam through a gate. The switch toggles between two latched positions to operate as a binary switch. By placing the switches in a matrix or an array coupled by fibre-optic collimators rendering divergent or convergent rays more nearly parallel, it is possible to control the passage of information through the matrix. In planar optical components, such a matrix can be realized by positioning the switches, each having a mirror or filter in a diagonal slot formed in the intersection of crossing light paths having ports facing the slot. The mirror is moved laterally to reflect incoming light from one fibre to an adjacent fibre communicating with the slot to perform a switching function. Such devices for e.g. a 4xc3x974 input/output switch module require a matrix of 16 switches, i.e. the number of required switches goes with the square of the input and output slots, if the matrix is symmetric in input and output slots. In the case of a 4xc3x971 or 2xc3x971 input/output switch module, the number of required switches is input x output
As mentioned, in optical systems, a light beam may alternate between travelling in free space and travelling in a fibre. This free-space-to-fibre coupling often occurs in the context of an optical switch. It is important for a switch that the free-space-to-fibre coupling be efficient to avoid unnecessary losses of light. Coupling efficiency is especially important in optical systems where light beams are sent through one collimated fibre to another collimated fibre. If the free-space-to-fibre coupling is not efficient then the amount of light coupled through the fibre might be insufficient for the intended purpose. Therefore to maximise the amount of light coupled to the fibre, it is desirable to make the switch as small as possible due to the limited distance through which a laser beam can travel in free space between two collimators. In addition a smaller switch design permits configuring more switch devices to form a single matrix or array of switches. Switch matrices can in turn also handle more switches, thereby permitting the design of more sophisticated gates.
However, current micro positioner design places limits on switch size reductions. Current micro positioners that produce a linear movement typically have a casing size of 11 mm in length with a 2 mm stroke. Permanent magnets are commonly arranged at opposite ends of the coils to hold a moving element in place (latched position) when the device is not energized. This requires space to prevent interference between the two different magnetic fields created by the two permanent magnets. This need for separation effectively places a lower size limit on micro positioners with two permanent magnets. Moreover, since the number of required switches in the matrix goes by the square of the input and output slots, respectively, the size of the switches can be an important feature for the realization of a planar optical component (e.g. a 16xc3x9716 input/output switch module requires already 256 switches). Therefore, although prior devices based on current micro positioners provide switching functions, they are difficult to manufacture and limited in the reduction of their size which causes the aforementioned problems. Furthermore, current micro positioners may be subject to temperature and environmental fluctuations, particularly because they employ materials that can expand and contract due to temperature fluctuations.
It is an object of the present invention to provide a smaller micro positioner which does not exhibit the above-described drawbacks. In particular, it should be possible for the positioner to maintain performance and reliability despite being of smaller size. It is a further object of the present invention to permit the micro positioner to be scaled down properly, maximise the efficiency of transmitting light through an optical component with a matrix of switches, reduce switching time to a maximum of 5 ms, and, as a final object, to also enhance reliability by the selection of low friction and low thermal expansive materials.
According to the present invention, this object is achieved particularly though the elements of the independent claim. Moreover, further advantageous embodiments follow from the dependent claims and the specification.
The objects of the invention are also achieved in particular in that an electromagnetic positioner or actuator comprises a piston, which piston is movable between a first and a second predefined position and which piston is held by a piston guide, the movable piston comprising a permanent magnet directed perpendicular to the direction of movement the piston comprising an electromagnetic coil, capable of polarity reversal, in the direction of movement of the piston, by means of which coil, in accordance with its magnetisation, the piston is movable from the one predefined position into the other predefined position, and the coil core, capable of polarity reversal, possesses a magnetic remanence by means of which the movable piston is fixable in one of the two predefined positions when the coil is switched off, i.e. not energized. The piston can be of cylindrical design with a cylindrical piston guide. It can also have a different shape such as, e.g. rectangular. The permanent magnet can be disposed on the piston at the end, for example, it also being conceivable for it to be integrated in the piston at a different place. It can be advantageous, if said permanent magnet and/or said electromagnetic coil are axially magnetized in the direction of motion of said piston. This has inter alia the advantage that the application of force by means of the magnet can be maximized. The permanent magnet of the piston can have e.g. an inductance (B) of 1.2-1.6 T and a coercive field of 940 000-1 000 000 A/m. This has the advantage that, with the typical dimensions for a micro linear positioner, it can correspond to the required signal strength. The magnet core, capable of polarity reversal, can consist e.g. at least partially of a semi-hard magnetic material. The piston and the magnet coil with magnetic core can be separated in the piston e.g. through spacers, which are installed between the piston guide and the magnet coil with the coil core. This has inter alia the advantage that during positioning the piston in the first position, the magnet coil with coil core are not damaged and a predefined spacing is kept between coil core and permanent magnet. In a preferred embodiment, the piston guide is achieved by means of a housing of the piston. Since, in contrast to the state of the art, a magnetic core, capable of polarity reversal, with remanence, is used, instead of two magnets, to bring the piston into one of the two positions, the piston can be of much smaller construction and more compact, which also means shorter reaction times for the piston. Smaller and more economical optical switches can also be created thereby.
In one embodiment, these objects are achieved by the invention in that an electromagnetic device is used which is composed of a permanent magnet and an electromagnetic coil mounted on a special half hard magnetic core. As we can reverse the polarity of the coil and of the special magnetic core, the magnet will either be attracted to the magnetic core, or be repelled from it. This results in a latched position in both directions. A ceramic cylinder and piston are attached to the coil core holder. The piston, with the magnet attached to it, is either attracted to the magnetic core, or is repelled from the magnetic core. Therefore as a function of the position of the actuator magnet, the piston is moved from one position to another. The piston moves a mirror or filter in one application of this micro positioner. The piston protrudes through one end of the ceramic cylinder. The cylinder guides reciprocating motion of the piston, its uppermost position is against a ceramic wedge and its lowermost position is against a ceramic ring. Energizing the electromagnetic coil operates the micro actuator. The actuator magnet is situated on the piston, and is in one of the two end positions, held or repelled by the magnetic core. Energizing the coil will either attract or repel the actuator magnet, this depends on the electrical polarity. The coil may later be energized in the opposite electrical polarity in order to move the magnet and piston in the opposite direction. This embodiment variant has the same advantages as the preceding one.
In one embodiment said piston is extendable axially outside of said housing of the electromagnetic positioner or actuator. This embodiment variant has the advantage, among other things, that the positioner is suitable for use in optical switch modules, an optical element, such as a mirror or filter, being installed on the part extending over the housing of the piston Therefore, in a further embodiment variant, the part protruding out of the piston housing comprises an optical element. The optical element can comprise a mirror and/or a filter element, for example. This has inter alia the advantages already mentioned. In the case of the previous embodiment variant, the protruding part can of course serve completely different purposes, such as e.g. the activation of a process, etc.
In another embodiment variant, the piston and/or the piston housing is made at least partly of ceramic. This has the advantage, among other things, that the friction resistance in the positioner can be greatly reduced and the components have a much smaller thermal expansion coefficient. On the one hand, this enlarges the possible field of application for the positioner. On the other hand, the wear and tear within the positioner is moreover reduced.
In a further embodiment variant, the piston comprises a lateral notching and the piston housing has a stop element by means of which the second predefined position of the piston can be set, the stop element abutting the piston at the notching. This has the advantage, among other things, that the positioner is easy to achieve and produce. This also brings with it, among other things, a reduction of the manufacturing costs.
In an embodiment variant, the stop element has magnetic properties which assist to hold the piston in the second position. This has the advantage inter alia that possible recoil momentum, occurring through the stopping of the piston in the second position, can be compensated.
In an embodiment variant, the magnet coil with magnetic coil core has an impulse time 2 to 3 times longer than necessary for moving the piston from one position into the other position. This has the advantage, among other things, that possible recoil momentum of the piston when impinging upon the spacer or the stop element can be compensated.
At this point, it should be noted that besides the micro linear positioner and the optical switches based on micro linear positioners according to the invention, the present invention also relates to a manufacturing method for such micro linear positioners and/or optical switches and/or optical switch modules.
Other features and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings, i.e. two embodiments of the present invention are described below by means of examples. The examples of the embodiments are illustrated by the following enclosed figures: